The overall objective of the proposed research is to understand neural mechanisms underlying auditory feedback processing and auditory-vocal interaction in the primate brain. Such mechanisms are important for both hearing and vocal communication, and the impairment of these mechanisms results in hearing and speech disorders. Few studies have investigated these neural mechanisms in non-human primates because of technical difficulties in studying the activity of individual neurons during natural auditory and vocal behaviors. We will use a unique model system, the common marmoset (Callithrix jacchus), to tackle these problems at the cellular and behavioral levels. The marmoset provides several important advantages over other non-human primate species: a rich vocal repertoire, a high reproductive rate while in captivity, and a smooth brain allowing easy access to all parts of the cerebral cortex. In this application, we plan to address three major questions along the research direction using novel techniques we have developed in the previous funding cycle. In Aim 1, we will study behavioral mechanisms underlying feedback-dependent vocal production in marmosets in order to determine the marmoset?s ability to voluntarily control their vocalization in real-time. Such evidence is crucial for understanding how marmosets use vocal feedback signals to guide vocal communication. In Aim 2, we will study how neurons in belt and parabelt areas of the auditory cortex process auditory feedback signals during vocalization. In Aim 3, we will attempt to dissect functional circuits in auditory-vocal interaction between frontal cortex and auditory cortex that are involved in auditory feedback processing. Findings from the proposed study will shed lights on neural mechanisms responsible for auditory feedback processing in the primate brain and have implications for understanding how the auditory cortex operates during active hearing and speaking in both normal and hearing- impaired listeners.